Journal Article

Cellular uptake of β<sub>2</sub>M and AGE‐β<sub>2</sub>M in synovial fibroblasts and macrophages

Kalisha D. O'Neill, Neal X. Chen, Mu Wang, Ross Cocklin, Yilong Zhang and Sharon M. Moe

in Nephrology Dialysis Transplantation

Published on behalf of European Renal Association - European Dialysis and Transplant Assoc

Volume 18, issue 1, pages 46-53
Published in print January 2003 | ISSN: 0931-0509
Published online January 2003 | e-ISSN: 1460-2385 | DOI: http://dx.doi.org/10.1093/ndt/18.1.46
Cellular uptake of β2M and AGE‐β2M in synovial fibroblasts and macrophages

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Background. Beta‐2‐microglobulin (β2M) amyloidosis is a destructive articular disease affecting dialysis patients. The amyloid deposits contain both β2M and β2M altered with advanced glycation end products (AGE‐β2M). We have shown that β2M increases the expression of matrix metalloproteinase‐1, vascular cell adhesion molecule‐1 and cyclooxygenase‐2 in human synovial fibroblasts, while the effect of AGE‐β2M in this model is markedly reduced. Conversely, in human monocyte/macrophages, AGE‐β2M stimulates cytokine release whereas β2M is less potent.

Methods. To understand why the two forms of β2M produce variable responses in different cells, AGE‐β2M was labelled with the fluorochrome Cy5, and β2M was labelled with the fluorochrome Texas Red (TR) and the uptake of 50 µg/ml of each was examined through live cell imaging at different time points using confocal microscopy.

Results. In human synovial fibroblasts, the AGE‐β2M‐Cy5 could be seen in endosome‐like structures inside cells by 45 min. After 3.5 h the distribution of endosome‐like structures had become perinuclear in nature and the concentration of AGE‐β2M‐Cy5 within these structures had increased. When a 20‐fold excess of AGE‐BSA was added to the synovial fibroblasts with the AGE‐β2M‐Cy5, the endosome‐like particles were not seen, suggesting competitive inhibition of uptake through an AGE‐receptor. In contrast, β2M‐TR progressively concentrated along the surface of synovial fibroblasts with minimal cellular uptake indicated by faint endosome‐like structures seen only after 8 h. Interestingly, in a different model, human and mouse monocyte/macrophages, the AGE‐β2M‐Cy5 and β2M‐TR had similar patterns of distribution and kinetics of uptake.

Conclusion. Our results suggest that β2M and AGE‐β2M are endocytosed via different mechanisms in human synovial fibroblasts and monocytes/macrophages. These results may offer a potential explanation of differences observed in cell culture experiments.

Keywords: advanced glycation; β2 microglobulin; dialysis amyloidosis; end products; endocytosis; macrophages; synovial fibroblasts

Journal Article.  4551 words.  Illustrated.

Subjects: Nephrology

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